Viscous liquid mixing apparatus



June 24, 1958 v w s VISCOUS LIQUID MIXING APPARATUS Filed April 5, 1956 INVENT OR THOMAS M. WILLS ATTORNEY ited States Paten fo 2,840,356 VISCOUS LIQUID MIXING APPARATUS Thomas Mason Wills, Wilmington, DeL, assignor to E. I. du Pont de 'Nemoursand Company, Wilmington, Del., a corporation of Delaware Application April '5, 1956, Serial No. 576,312

2 Claims. (Cl. 2599) This invention relates to fluid mixing apparatus and, more particularly, to apparatus for mixing or homogenizing a stream of viscous liquids.

An object of this invention is to provide improved means for rapidly and thoroughly mixing or homogenizing a continuous stream of viscous liquids. A further object is to provide improved apparatus for rapidly and thoroughly blending or homogenizing viscous molten polymeric materials flowing in a continuous'stream originating from at least two sources of molten polymer. A still further object is to provide apparatus effective to efiiciently homogenize viscous liquids, e. -g., molten polymers of different viscosities, as they travel at relatively high rates through pipe lines; The foregoing and additional objects will more clearly appear from the description which follows.

These objects are realized by the present invention which, simply stated, comprises, in combination, an elongated cylindrical vessel-having liquid inlet means in one end thereof and liquid outlet means in the opposite end thereof, a driven shaft in said vessel extending longitudinally thereof and coaxially therewith and a multiplicity of flat-faced rotors in face-to-face contact with one another and fixed'to "said shaft "to rotate "therewith, each of said rotors having four identical protuberance's forming turbine-like, fiat-facedwanes, each of said vanes on alternate rotors having a substantially concave leading edge and a tip surface conforming to the inside surface of the cylindrical vessel'and closely spaced from said surface, each of the vanes on the remaining rotors having a substantially convex leading edge and a curved tip surface having a curve conforming to the inside curved surface of the cylindrical vessel and closely spaced from said surface, said rotors and their corresponding vanes having a thickness about 0.3 of the inside diameter of the vessel, and the vanes of alternate rotors being out of phase, i. e., displaced, by about 45 from the vanes of the adjacent rotors.

Referring now to the accompanying drawings wherein:

Fig. l is a side view, partly in section, of mixing apparatus comprising the features of the present invention,

Fig. 2 is a cross-sectional view on the line 2-2 of Fig. 1, and

Fig. 3 is a front elevation of the preferred form of rotor.

An elongated cylindrical vessel 1, preferably jacketed to permit thermal control of the viscous liquids flowing therethrough, is provided at one end with a liquid inlet opening 2 which, in the preferred embodiment of the invention, is so disposed that the liquid enters the mixer substantially at right angles to the longitudinal axis of the vessel, and is provided at the other end with a liquid outlet 3 which, preferably, is in line with the longitudinal axis of the vessel 1. A rotary shaft 4 whose axis is concentric with the longitudinal axis of the mixing vessel, extends for substantially the entire length of the'vessel, and is journaled at one end in spider bearing 5 adjacent I 2,840,356 Paiented June 24, 1958 '2 to outlet opening 3 and at its opposite end is supported in and suitably keyed to a hollowed drive shaft 6 which is, in turn, carried in bearing 7 fitted in the end wall of vessel 1 adjacent the inlet 2. The drive shaft 6 is driven by any convenient means (not shown).

A multiplicity of rotors 8, 9, 10, 11, 12, 13, 14 and 15, each consisting of a flat'plate of metal which has been machined and/or cast to form a disc-like structure having a hole in'the middle and four identical protuberances which are in the form of turbine-like curved vanes, are keyed to a drive shaft for rotation therewith, each rotor being mounted in close contact with adjacent rotors so that there is substantially no space between adjacent facesof the rotors. The rotors are so mounted thatthe vanes of alternate rotors, e. g., rotors 8, 10, 12 and 14 curve oppositely to the vanes of the rotors therebetween, i.-e., rotors 9, 11, Band 15. The rotor structure is preferably integral, that is, machined from an initially flat metal plate. However, the structure may be composed of a multiplicty of. parts wherein individual vanes are attached, by bolts, for example, onto a ring which would be keyed to the drive shaft.

The rotor illustrated in Fig. 3 is a typical andpreferred construction within the scope of this invention; each vane of the rotor comprises a concave edge A, a convex edge B, and a curved tip edge C, curved to fit the contour of the inner wall of the vessel 1. If this rotor were rotated in the directionof the solid arrow, the leading edge of the rotor-vane would be illustrated by edge A, this being substantially concave incontour. The trailing edge, therefore, would be edge B. In the assembly shown in l, the rotorsadjacent to the rotor just described would have reversed edges, i. e., concave edge B is the leading edge of the vane and the trailing edge is A.

An angular separation'or displacement of about 45 between vanes of adjacent rotors, as shown in Fig. 2, was found to be critical for the mixing apparatus of the present invention. Another factor critical to this invention pertains to the relationship between the thickness of the rotors and the inside diameter-of the cylindrical vessel.

of the rotor), 'be about 0.3 of the inside diameter of the cylindrical vessel. These critical limitations of angular separation and thickness of the rotors have been found to influence mixing efficiency of the apparatus, and optimum efliciency under substantially all circumstances is obtained when these specifications are incorporated into the apparatus design.

It is also requisite that there be close clearance between the tip surface of each vane and the inside surface of the cylindrical vessel. Preferably, the clearance between the tip surface of each rotor and the inside surface of the cylindrical vessel is in the neighborhood of 0.01- 0.06", but it could be less or could be as much as 0.25.

Mixing in the present apparatus is believed to be caused by fluid shearing. Each vane of the rotors forms a vortex; and the centers of the vortices formed by vanes having leading edges designated by A are in a different position relative to the centers of the vortices formed by vanes having leading edges designated by B. Since these vortex centers do not coincide, the relative motions of fluids influenced by vanes of alternate rotors do not coincide; and fluid shearing occurs.

The mixing efficiencies of the apparatus of the present invention were determined by employing a photometric 1 ployed usingS rotors and an agitated length of 12".

paratus was tested by operating it under various conditions, such as varying rates of rotor rotationyvarying linear flow of viscous material through the apparatus, varying degrees of. angularseparation between vanesof adjacent rotors, etc. The negatives of photographs taken of the blended liquids immediately downstream of the mixing apparatus werefscanned on a microphotometer to measure the" density variations in the negatives caused'by the variations in the jcolor of the dyed mixture of viscous liquids. I d

In order to set up a density standard, an'arbitrary linear relationship wasassumed using completely mixed samples and substantially :unmixed samples. The completely mixed samples had a chart variation of 1.0 centimeter (deflection of the microphotometer recording needle) or less and were designated as 100% mixed, and the unmixed samples had, a variation of approximately 8 centimeters and were designated as mixed. Mixtures of a dyed viscous liquid and a colorless viscous liquid intermediate between the two extremes were assigned .values expressed in terms "of percent mixing efficiency between (land 100%.

An apparatus, such as is shown in l, was em- The inside diameter of' the. cylindrical vessel was and each ,of the rotors was 1 /2 in thickness. This apparatus j was employed to blend 1 part of a red dye with parts of viscous corn syrup (having a viscosity of 2,0003,000 poise). To test the apparatus, the rate of syrup flow was varied from, 500 lbs./hr. to 1500 1bs./hr., and the rate of rotation of the rotors wasvaried from revolutions/ minute to 120 revolutions/minute. At a syrup flow of 500 lbs./hr., a mixing efficiency of 100% was obtained at 60, and 120 revolutions/minute respectively. At

a syrup'fiow of 1,000 lbs./hr., mixing efficienciesiof were obtained at 60, 90 and revolutions/minute. At

a syrup flow of 1500 lbs./hr., a mixing efiiciencyof'74% was obtained with a rate of rotation of 60 revolutions/ minute, while 90 and 120 revolutions/minute gave mixing efficiencies equal to 100%. t

Actually, it appeared to be more difficult'to blend small amounts of coloring agents with larger amounts of syrup than it was to blend, for example, equivalent portions of dyed syrup and-colorless syrup in mixing apparatus within the scope of this invention. Therefore, the above-described tests were rather severe and indicated a rather accurate picture of the efliciency of the mixing apparatus. d

homogenization of viscous liquids as they travel at relatively high rates through pipe lines, the essential advantage of the present apparatus is its capacity to effect highly efficient agitation, and, consequently, homogenization of such viscous liquids in relatively short lengths By realizing the tortuous path through which the liquids must travel in traversing the present apparatus, it is readily evident as to the reason for its high efficiency. A further advantage of the apparatus is that it is relatively easy and economical to construct and assemble. r

I claim: 7

1. Apparatus for homogenizing a stream of viscous liquid comprising an elongated cylindrical vessel having a liquid inlet opening at one end and a liquid outlet opening at the opposite end, a driven shaft extending centrally of said vessel and for substantially the length thereof, a plurality of fiat-faced rotors mounted face-tofrceon, and driven by said shaft, each of said rotors mounted in contact with adjacent rotors and having four identical equally spaced flat-faced curved vanes lying in 'a plane perpendicular to the axis of said shaft, each vane having a curved leading edge and terminating in a curved tip edge corresponding in curvature to the curvature of the inside curved wall of the vessel and closely spaced from said wall, the vanes of each rotor having leading edges oppositely curved to the leadingedges of the'vanes of the rotors in contact therewith, said rotors and their vanes having a thickness about 0.3 of the inside diameter of the vessel, and the vanes of alternate rotors being displaced about 45 from the vanes ofthe rotor 'therebetween.

2. Apparatus according to claim 1 wherein the inlet opening is located on theside of said vessel whereby viscous liquidsenter said'vessel substantially at right angles to the axis of said driven shaft.

References Cited in the tile of this patent UNITED STATES PATENTS 751,187 Lewiak Feb. 2, 1904 1,087,415 Welton Feb. 17, 1914 2,538,466 Marco Jan. 16, 1951 1 FOREIGN PATENTS 556,349 Great'Britain Sept. 30, 1943 

1. APPARATUS FOR HOMOGENIZING A STREAM OF VISCOUS LIQUID COMPRISING AN ELONGATED CYLINDRICAL VESSEL HAVING A LIQUID INLET OPENING AT ONE END AND A LIQUID OUTLET OPENING AT THE OPPOSITE END, A DRIVEN SHAFT EXTENDING CENTRALLY OF SAID VESSEL AND FOR SUBSTANTIALLY THE LENGTH THEREOF, A PLURALITY OF FLAT-FACED ROTORS MOUNTED FACE-TOFACE ON, AND DRIVEN BY SAID SHAFT, EACH OF SAID ROTORS MOUNTED IN CONTACT WITH ADJACENT ROTORS AND HAVING FOUR IDENTICAL EQUALLY SPACED FLAT-FACED CURVED VANES LYING IN A PLANE PERPENDICULAR TO THE AXIS OF SAID SHAFT, EACH VANE HAVING A CURVED LEADING EDGE AND TERMINATING IN A CURVED TIP EDGE CORRESPONDING IN CURVATURE TO THE CURVATURE OF THE INSIDE CURVED WALL OF THE VESSEL AND CLOSELY SPACED FROM SAID WALL, THE VANES OF EACH ROTOR HAVING LEADING EDGES OPPOSITELY CURVED TO THE LEADING EDGES OF THE VANES OF THE ROTORS IN CONTACT THEREWITH, SAID ROTORS AND THEIR VANES HAVING A THICKNESS ABOUT 0.3 OF THE INSIDE DIAMETER OF THE VESSEL, AND THE VANES OF ALTERNATE ROTORS BEING DISPLACED ABOUT 45* FROM THE VANES OF THE ROTOR THEREBETWEEN. 